On December 30, 1872, off Vigo, Spain, the
Challenger's scientific voyage began in earnest as they conducted the
first dredging operation.

Sighted the coast of Spain
this morning but are still 150 miles from Lisbon. At 10 o'clock this
morning the first cast of the dredge was made & bottom obtained at
1500 fathoms but in hauling up the dredge 100 fathoms of line was
lost over board. The dredge was again cast but came up bottom upwards
but on another attempt being made they succeeded in bringing up mud
and several species of Fish from a bottom of 1125 fathoms, or nearly
1 1/2 miles; on the mud being analysed numerous insects were found
in it--the fish are preserved in bottles. The Dredge is of Iron &
not unlike a pig trough with a net over it & weighs with the weights
attached several hundred weight. The strain on the line is very great
as it reaches the bottom & to ease it, several gutta percha ropes
are spliced to it which will stretch when strained. The Dredging line
is about the thickness of a man's two fingers. When dredging the Ship
is hove to, & the Dredge is let down from the main yard & hauled up
by a small steam engine & the line coiled away on the upper deck to
dry; 1200 fathoms of line will take one hour in reaching the bottom
& 3 hours in hauling up.

Two of Challenger's modern power features would best be
used during the dredging operations. The steam engine, which assisted
the corvette's sails when necessary in moving the ship, were run constantly
during dredging to help the ship hold a steady position while the dredge
and its thousands of feet of line were lowered and reeled in.

The small donkey engine on the deck was used to haul in
the dredge lines, a formidable task had it been necessary to complete
it by hand.